1. Field of Invention
Various embodiments of the present invention relate to optical communication, and more particularly, to a superluminescent diode that is a light source of a wavelength tunable laser and a method for implementing the same.
2. Description of Related Art
In order to implement an economical WDM (wavelength division multiplexing) subscriber network system, it is essential to develop a stable and economical light source. Especially, since in a WDM subscriber network system, communication is made with each subscriber dedicated with a certain wavelength, research is needed on a wavelength-independent light source that is capable of providing a same light source to subscribers regardless of their dedicated wavelengths.
As part of an effort to develop such a colorless light source, a WL FP-LD (wavelength-locked Febry-Perot Laser Diode), RSOA (reflective semiconductor optical amplifier), and PLC (planar lightwave circuit)-ECL (external cavity laser) are actively studied these days.
Of the laser diodes used as light emitting elements in optical communication, an FP-LD (Febry-Perot Laser Diode) is inexpensive and easy to manufacture. However, an FP-LD generates a plurality of longitudinal modes, and thus it is difficult to be applied to long-distance transmission and WDM transmission. As an alternative to an FP-LD, there is a DFB-LD (Distributed Feed Back-Laser Diode) that has a narrow line width and generates single mode characteristics with stability, but a DFB-LD is expensive and difficult to manufacture.
Thus, as an alternative, various types of external cavity lasers were proposed. Such an external cavity laser is characterized to resonate in a single mode where longitudinal modes of an FP-LD overlap a mode of an external cavity, and to have excellent wavelength selectivity and temperature stability. However, most external cavity laser structures use an optical bragg lattice, and is thus either complicated or requires high precision to manufacture, making it difficult to be applied to low cost commercial products.